The present invention relates to a system and a method for examining an object. In particular, this invention relates to a system and a method for examining an object containing a flowing liquid. Further, this invention relates to a system and a method for examining a blood motion in a body part of a patient. In particular, this invention relates to a system and a method for displaying functional regions in a brain of a patient.
From the state of the art it is known to exploit the so-called “Doppler effect” to optically examine a motion of particles in a liquid. Thereby, measuring light is directed to a region of a body part of a patient to be examined. The measuring light penetrates some millimeters into the region to be examined and interacts with matter in the region within a penetration depth of the measuring light. Among other things, the measuring light is reflected from particles moving relative to each other, wherein the measuring light experiences a change of a wavelength compared to the wavelength of the measuring light being incident, wherein the change depends on the motion of the reflecting particles, in particular on the motion of blood cells. These changes of a wavelength of the reflected measuring light may be determined by detection using an appropriate detector. The basic principles for this so-called “laser Doppler method” are described in Stern, “In vivo evaluation of microcirculation by coherent light scattering”, Nature, Vol. 254, pages 56-58, March 1975. Information about a motion of particles in a liquid are also referred to as perfusion data or perfusion in the following.
U.S. Pat. No. 4,109,647 describes how one may obtain information about the velocity of red blood cells at one point of a body part to be examined using this method.
U.S. Pat. No. 5,361,769 describes a scanning method for measuring blood perfusion of a body part to be examined. Thereby, a laser beam scans the body part to be examined, wherein the reflected signal is detected by a detector.
US 2005/0187477 A1 describes a laser-Doppler-perfusion imaging system to gain perfusion related data of a sample. The body part to be examined is illuminated across an area using laser light and the illuminated region is imaged to a detector extending in an area. From a plurality of such recorded images of the body part to be examined, information about a concentration of moving particles and about a velocity of particles moving relative to each other or relative to fixed structures in a sample volume which is associated to each pixel of the detector can be gained.
However, it became apparent that the previously described systems and methods often do not provide satisfying results.
For displaying and identifying functional regions in a brain of a patient so far a number of techniques have been used. In particular, it should be mentioned: functional magnet resonance tomography, electroencephalography, positron emission tomography and others. Due to the “blood oxygen level dependent (BOLD)-effect”, it is possible in principle to detect a contrast in a body part to be examined due to the presence or non-presence of oxygenated and deoxygenated, respectively, hemoglobin using magnet resonance tomography. However, this method is very cost consuming and time consuming. Due to a long data recording time required by this method motions of the body part to be examined may occur during data recording. This in turn leads to difficulties in an evaluation of the data, in particular by the rotations and translations associated therewith, or also deformations of the data sets relative to each other which have to be determined to align the data relative to each other.
Thus, there is a need to provide a system and a method diminishing the above-mentioned disadvantages.